The Biomechanics of Bruising
Heather Black1, Sylvie Coupaud1, Niamh NicDaeid2, Philip Riches1
1Department
of Biomedical Engineering, University of Strathclyde, Glasgow
2Centre for Anatomy and Human Identification, University of Dundee, Dundee
([email protected])
Methods
Introduction
Haemoglobin concentration[1], photographic[2] and
colour pattern identification[2,3] have been used for
characterising contusions. However, few studies
specifically focus on the mechanics of bruise
formation[2,4]. Ultimately, we wish to determine if
there is a link between the time progression of
bruising and mechanics of impact, which necessitates
controlled impact generation. Several studies have
used a paintball marker[3, 5-7], yet to date their
suitability has yet to be assessed. Therefore, this
study aimed to determine if a BT-4 Combat marker is
suitable for generating controlled blunt impacts.
A fully pressurised marker (~3000
psi), was secured via a table
mount and reusable paintballs
(mass of 2.6 g) were fired
through a chronograph (Figure 1),
until the cylinder depressurised.
This procedure was repeated a
further 5 times to determine the
repeatability of firing velocity.
To determine accuracy, carbon
paper targets were placed at
distances of 4, 5, 6, 7 and 8 m
and 40 shots were fired at each.
Figure 1. Experimental set-up of the marker and
chronograph
Results and discussion
Above 800 psi the marker velocity is effectively constant, whilst below this value,
velocity decreases with pressure (Figure 2). There was no significant difference
between the 6 tests and above 1500 psi, the average velocity was 71.27 ± 0.529 ms-1.
3000
2500
Approx. Pressure (psi)
2000
1500
1000
500
0
90
80
Velocity (mps)
70
60
Figure 3. Examples of impact overlap and increasing
dispersion at 4 and 6 m
Test 2
50
Test 3
40
Test 4
30
Test 5
20
Test 6
0
10
0
0
100
200
300
Shot No.
400
500
600
Distance (m)
x sd (cm)
y sd (cm)
4
1.45
1.87
5
1.79
2.15
6
2.77
2.72
7
2.31
3.74
8
2.15
2.28
Average
2.09
2.55
Table 1. x and y standard deviations around the
mean impact location
Conclusions
0
-2
-4
-6
-8
-10
-12
-14
-16
-18
-20
-22
-24
-26
-28
-30
-32
-34
2
4
Distance (cm)
6
8 10 12
14
16
18
8m
7m
6m
5m
4m
Laser
Figure 4. Average impact location ± x and y standard deviations for each
target distance
References
[1]
Impact velocity and location were highly predictable. Thus the
paintball marker is appropriate for use as a controllable,
repeatable and reliable method for blunt impact generation.
Combined with imaging techniques such as infrared and cross
polarisation photography, this will allow for both the mechanics
of impact and the aging of bruise injuries to be investigated.
Distance (cm)
Figure 2. Firing velocities for all 6 tests
From 200 shots, the impact location of 177
were successfully recorded with impact overlap
resulting in lost data (Figure 3). Marker
trajectory and laser sight were divergent
(Figure 4) resulting in predictable vertical
(~2cm/m) and horizontal (~1 cm/m) error. The
effect of gravity on marker impact location was
not apparent. Impact dispersion increased with
distance (Figure 3, Table 1).
6m
4m
Test 1
[2]
[3]
[4]
[5]
[6]
[7]
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